Reserve type electrochemical battery



Aug. 24, 1965 o. T. ADLHART ETAL 3,202,548

RESERVE TYPE ELECTROCHEMICAL BATTERY Original Filed Nov. 5, 1960 SOURCEINVENTORS, OTTOADLHART 8 HOWA Rw A T TRVEK United States Patent O3,202,548 RESERVE TYPE ELECTRCHEMICA@ BATTERY @tto T. Adlhart, Orange,and Howard l. Knapp, Red NJ., assignors to the United States of Americaas represented by the Secretary of the Army Continuation of applicationSer. No. 623.455, Nov. 3, 105i?. This application Aug. 30, 1962, Ser. N220,972 1 Claim. (Cl. 13S- 90) This application is a continuation of theapplication of Otto Adlhart and Howard R. Knapp, Serial Number 67,- 145,led Nov. 3, 1960, now abandoned, for Reserve Type ElectrochemicalBattery.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, Without the payment of anyroyalty thereon.

This invention relates to an improved electrochemical battery utilizinga liquid anhydrous ammonia electrolyte, and more particularly, to areserve type electrochemical battery that can be activated by a liquidanhydrous ammonia electrolyte.

The objective of this invention is to provide a reserve typeelectrochemical battery that can be activated and then operate in a veryshort time at temperatures from about 60 C. to 70 C.

The principle of reserve type operation offers, as is widely recognized,the advantage of almost unlimited battery shelf life. It is based on theconcept that electrolyte and cell compartments are separated up to themoment when the battery is actually used. The design of a reserve typebattery as well as the activation device may vary widely. In most cases,however, the electrolyte is kept in a container which may have a tubularshape and is separated from the cell compartments by a diaphragm. At themoment of activation, the diaphragm is burst by the pressure developedfrom the firing of a squib located in the electrolyte container and theelectrolyte is forced into the battery. Many other techniques have alsobeen used successfully to bring the electrolyte into the cellcompartments.

These techniques have generally given satisfactory results at normal andwarm temperatures. At low temperatures, however, appreciablediiiiculties occur. These difliculties can be attributed to the factthat conventional battery systems have to be heated in order to beoperable at low temperatures. In reserve type batteries, this is done byelectrical heating coils that surround the battery. It also is achievedin many cases by chemical heating devices either located on the batteryplates or in the electrolyte container. On the activation of such abattery at low temperatures, considerable delay cannot be preventedbefore the battery is operable. This is due to the time needed for theheat transfer and the temperature control that has to be provided inorder to avoid overheating of the battery. The delay between activationand actual operation of the battery may be as long as 30 minutes. Onlyunder very favorable circumstances can it be reduced to 3 4 seconds at atemperature of 40 C. This, however, is insuflicient since in manyapplications activation has to be completed in less than a second.

We now find that the diiculties of low temperature activation can beovercome by using a liquid anhydrous ammonia electrolyte and a type ofbattery cell construction as will be described hereinafter. That is,with this type electrolyte and battery cell construction, a reserve typeelectrochemical battery can be activated without heating devices in lessthan a second at temperatures as low as -70 C. This, of course, enablesour system to be used in many military as well as commercialapplications where electronic equipment has to be brought in opera tioninstantly.

hd Patented Aug. 24, 'i965 In preparing the liquid anhydrous ammoniaelectrolyte, a salt ionizable in liquid anhydrous ammonia is dissolvedtherein. Any salt can be used regardless of the neutral, acid oralkaline character which it imparts to the solution. Examples of saltsof general applicability are the thiocyanates, perchlorates,lluoborates, cyanates, nitrates, nitrites, and the like. The salt may bepresent in the amount of about 15% to 45% by weight of the totalsolution. The use of potassium thiocyanate as the salt of the liquidanhydrous ammonia electrolyte is preferred in the electrochemicalbatteries.

ln the case of the reserve type battery the preformed liquid electrolyteis placed in an electrolyte container which is inert to the ammoniasolution. Aluminum, stainless steel, iron and even plastics are amongthe materials that can be used for this purpose.

The cell compartment of the reserve type rapid activating ammoniabattery employs sheet anodes, pasted cathodes and a plastic spacer forelectrode separation. The plastic spacer is particularly important inhigh rate batteries Where high current densities are drawn from the cellat the moment of activation. This spacer allows fast penetration of theelectrolyte solution throughout the cell. The spacer can have variousshapes. That is, it can be a corrugated and perforated plastic sheet forexample, o1' a screen of plastic bars with wide openings in order toprovide free flow of the electrolyte and minimum internal cellresistance. Such a spacer provides for the maintenance of maximum freevolume between the anode and the cathode of the cell compartment, andalso provides for minimum contacting surfaces between the faces of theanode plate and separator and between the faces of the cathode plate andseparator. The maximum free volume is essential to allow for expansionof the anode and cathode plates due to formation of cell reactionproducts formed by initial reaction with the electrolyte or through celldischarge, to provide minimum cell resistance, and to provide maximumionic mobility in the electrolyte. In low rate reserve type batteriesand nonreserve electrochemical batteries, a cell construction withoutplastic spacers is usable since the initial current densities are not asgreat. Simple separation of the electrodes by several layers of paper isthen suiicient.

Essentially, the reserve Itype rapid activating ammonia battery cellcompartment will consist of a three-plate sandwich design with thecathode in the center, a separator or spacer on either side lof thecathode and a thin metal anode placed against the outside of eachseparator. The anode can be an electropositive metal; in general, ametal above iron in the electrochemical series, particu= larly lithium,sodium, potassium, caesium, Zinc, aluminum or beryllium. The use ofmagnesium as the anodic material is preferred. The cathode consists of aflat plate design in which a depolarizing compound is thoroughly mixedwith non-reactive conductive material such as `graphite or carbon blackto provide adequate conductivity to the plate. An organic binderdissolved in toluene is added and the mixture pasted on both sides of anexpanded metallic grid structure. The cathode is then placed in a porouspaper envelope such as Aldex paper to prevent mechanical ilaking of thecathode material from interfering with the electrochemical action of thecell. The use of a heavy metal sulfate such as the sulfates of lead ormercury as the depolarizing compound is preferred. Then too, thematerial of the metallic grid structure must be non-reactive with theliquid ammonia electroly'te. Materials such as titanium, silver,aluminum, or stainless steel serve the purpose well.

The principle of reserve type operation utilizing liquid anhydrousammonia electrolyte can perhaps be best seen by referring to thedrawings.

In the drawings, FG. 1 is a schematic or diagrammatic View showing acontainer holding liquid anhydrous ammonia electrolyte, cellcompartments of a reserve type electrochemical Y battery sepa-rated fromthe container by a diaphragm, and means for rupturing the diaphragm.

FIG. 2 is a cut away view of a 2 plate cell compartment of :a reservetype electrochemical battery for rapid rate activation.

FIG. 3 is a cross-sectional View of a 3 plate cell compartment of areserve typel electrochemical battery for rapid rate activation.

FIG. 4 isacross-sectional view of a 3 plate cell compart-ment of :areserve type electrochemical battery for low rate activation.

Referring to FIG. l of the drawing, the preformed liquid ammoniaelectrolyte 2 is placed in the electrolyte container. VAt the desiredtime of activation, application of pressure from che pressure source 3causes rupture of the diaphragm 4 whereby the electrolyte flows into thecell compartments of the reverve type electrochemical batte-ry 5.

Referring to'FIG. 2 of the drawing, the cathode 14 consists of a atplate design pasted on both sides of an expanded grid structure 15. Thescreen of plastic bars with Wide openings 16 separates the cathode fromthe thin sheet anode 1'7.

In FIG. 3 of the drawing, a corrugated and perforated plastic sheetspacer 16A separates the thin sheet anodes 17, from the cathode 14. Y

In FIG. 4 of the drawing, a pad from several layers of filter paperimpregnated with electrolyte salt 18 separates the sheet anodes 17 fromthe cathode 14. YIn both :the rapid rate and low rate activation systemsshown, the use of the liquid anhydrous ammonia electrolyte assures lowtemperature operation without auxiliary heat, and the cell structuredesign allows immediate contact of the electrolyte with all cellcomponents. Significantly, it has been found that activation with liquidammonia electrolyte assures more complete and rapid activation of thecell than activation by ammonia Vapor. That is, at low temperatures,activation by ammonia vapor was incomplete because part of theelectrolyte V4pad was left dry and moreover, resulted in uncontrollableformation of highly concentrated salt solutions. rthat causedirnrnediate anode polarization. ,Complete activation with liquid ammoniaelectrolyte can be obtained at any temperature of battery operation.

In deciding upon a suitable ammonia system for rapid rate and low rateactivation many factors have to be considered as influencing theperformance. These includes the chemical properties of the electrolytesolution, the conductivity of the electrolyte, and the corrosion,solubility, potential, andA current carrying :ability of the anode andcathode materials, Among the anode materials us-Y -able inammoniasyStemS, magnesium is especially preferred because it is notsoluble in liquid ammonia.V When using magnesium as the anode, certainelectrolytes andV cathodic materials are found to be preferable ltoothers.

As far as the electrolytes are concerned, magnesium salts generally formpoor conductive electrolyte solutions in anhydrous ammonia. If systemswith this electrolyte are discharged at a high current density, a greatdrop in cell'voltage is unavoidable because of the high resistivity oftheV electrolyte. Consequently,the energy output Yof the system isdrastically reduced, The useV of ammonium salt solutions presentanotherproblem. That is, the ammonium salts form acid solutions in anhydrousammonia.V Highly active materials such as magnesiuml therefore arerapidly dissolved in these solutions with the formation of hydrogen anddissolution of the anode. Due to this rapid corrosion, ammonium saltelectrolytes cannot anode.

be usedin low rate systems with magnesium anodes. At J high rates, alimited use is possible. However,v even there, a high 108s v.in capacitycannot be avoided. Best results are obtained using'an electrolyte salttha-t forms neutral solutions in liquid ammonia. The alkali metal saltswork well in this connection and particularly desirable results areobtained with potassium thiocyanate. That is, use yof these electrolytesin systems with magnesium anodes results in a large reduction in theinternal volta-ge drop and elimination of the corrosion of the anode andconsequently gassing and loss in capacity. In fact, the voltage drop'isreduced to about l that observed with magnesium salt electrolyte and themagnesium anode is found to be completely stable over long periods oftime in alkali metal solutions.

As concerns the cathode material to be used when magnesium is the anode,the use of inorganic oxides and heavy metal chlorides or thiocyanatescause serious problems. Oxides will generally give satisfying serviceonly in acid ammonia solutions. solutions are entirely unsuited formagnesium anodes because of rapid chemical corrosion. The heavy metalchlorides and thiocyanates are not desired because of their solubilityin ammonia electrolyte solutions. Heavy metal ions travel tothe anodeand react directly with the mag nesium which results in loss in cellcapacity and polarization of the anodes. thev use of mercuric chlorideat room temperature as a cathodic material will only be utilized byabout 17% for the desired' electrochemicalreaction. The remainingmaterial will be lost in a direct chemical reaction with the The adverseeffects of oxides, thiocyanates and chlorides can be avoided by usingheavy metal sulfates for depolarization. Mercurio sulfate and leadsulfate Work particularly well, that is, theyV are appreciably lesssoluble than the previously mentioned thiocyanates and chlorides.Because of this lower solubility, self discharge is greatly reducedV insystems with magnesium anodes. With mercuric sulfate for'instance, up to90% of the active material is utilized for theV desired electrochemicalreaction compared to 17% with the mercuric chloride.'

Consequently, the energy output of systems with magne-V tage of heavymetal sulfates is their operability in neutral' ammonia solutions whereheavy metal oxides are not suitable. These solutions are as previouslystated highly suitable for magnesium anodes and contribute toward goodutilization ofthe cell capacity at'low as well as high discharge rates.V

The following examples illustrate cell systems of the reserve typeelectrochemical battery.

Example I The anode is made of a thin sheet of magnesium which ispickled with acid and Vpolished with steelwool. The cathode consists fofa mixture of 70% mercuric sulfate and 30% graphite pasted with theaddition of a small amount of organic binder on a silver, titanium,tantalum or stainless steel grid. As electrolyte, a 15% to 45% solutionof potassium thiocyanate in'liquid anhydrous ammonia is used. The use ofa 35% solution is preferred. Y

The cell is made of one Ycathode and one anode as illustrated by FIG. 2of the drawing. They are separated by a plastic spacer approximately0.04 inch thick; This barrier allows free ow of the electrolyte.V Toincrease me-V chanical stability of the cell and improve separation ofnegative andV positive material, the cathode is wrapped in one or morelayers of thin porous paper.

For discharge at low temperatures the cell is immersed 'in theelectrolyte, or the electrolyte is poured into the cell. VAt highertemperatures, the electrolyte is brought into contact with other cellcomponents under pressure. At 60 VC. a load voltage of 1.9-2.0.volts isobtained at a current density of 1 ampere per square inch. The ,cellproduces current for at least 6 minutes with a cell voltage higher than1.75 volts. At 70 C.,/where the cell. has to be discharged underpressure, a voltage of 2.0-2.1

is observed at 1 ampere per square inch. Again, the servV As statedpreviously, however, these Because'of this reaction for example,

age. At both temperatures, the utilization of the cathode material atthe above-mentioned rate is in the order of 65-85% of the theoreticalvalue of 2 Faradays per mole. The utilization of the anode materialapproaches 100% of theoretical value. The energy output of the cell isapproximately 2030 watt hours per pound and 1.5-2.0 watt hours per cubicinch.

Example 2.-ln this example, the same anode and cathode material andelectrolyte are used as in Example 1. The cell, however, is made ofthree plates, one cathode and 2 anodes as illustrated by FIG. 3 of thedrawing. The cathode is placed in the center ot the cell and on eachside is placed a plastic separator and the anode. Anode and cathodeplates as well as electrode spacing and separation are identical withExample 1.

The cell is discharged at a current density of 0.2 amperes per squareinch of apparent cathode surface. The load voltage is 2.3 Volts at thebeginning of discharge. lt drops to approximately 2.07 volts after 20-25minutes discharge.

At 70 C., almost the same length of service is obtained at a voltagelevel only 2-3% higher than at 60 C. Utilization of the active cathodematerial is in the order of 'l0-85%.

Example 3.-In this example, magnesium is the anode, a 35% by weightsolution of potassium thiocyanate in anhydrous ammonia the electrolyteand lead sulfate is the cathode material. The cell structure isidentical to that in Example l. That is, magnesium sheet anodes, plasticspacers, and thin paper separators are employed.

The cathode is prepared of pure lead sulfate powder or a mixture of leadsulfate and graphite. This material is pasted with the addition of someorganic binder on similar metal grids as in Example 1.

At -60 C., a two-plate cell can be discharged at a current density of 1ampere per square inch. At least 4 minutes of service is obtained lat aload voltage starting at 1.5 volts at the beginning of the discharge to1.3 volts at the end of discharge. The utilization of the activepositive material is at least 50% of the theoretical value ot twoFaradays per mole.

Example 4.-'I1his example illustrates a low rate discharge of a systemutilizing a magnesium anode, a solution of potassium thiocyanate inanhydrous ammonia as the electrolyte, and mercurio sulfate as thecathode. The cathode consists of a mixture of graphite and 90% rnercuricsulfate pasted on a silver, titanium, tantalum or stainless steelscreen.

oase-e Negative and positive plates are separated by one or severallayers of filter paper impregnated with potassium thiocyanate asillustrated by FIG. 4 of the drawing. The concentration of potassiumthiocyanate in the pads can be varied widely. Any amount of salt whichcan produce electrolyte having a salt concentration between 5-60% oyweight can be used. For discharge, the cell is immersed in pure ammonia.At C. the electromotive force of the cell is approximately 2.38 volts.It will rise to 2.45 volts at C. The cell is discharged at 10milliamperes per square inch. At least 10 hours of service are obtainedat a load voltage above two volts.

lt will be obvious to those skilled in the art that various changes andinodiications may be made therein without departing from the inventionas herein claimed.

What is claimed is:

A reserve type electrochemical battery that can be activated withoutheating devices in less than one second at temperatures of 70 C., saidbattery including a container holding a liquid anhydrous ammoniasolution of potassium thiocyanate therein, a cell compartment separatedfrom the container by a diaphragm, means for rupturing said diaphragm sothat the liquid anhydrous ammonia solution of potassium thiocyanate canenter said cell compartment, and where said cell compartment comprises amagnesium anode and a cathode including an expanded metallic gridstructure having a mixture pasted on both sides thereof and wherein saidmixture is of a depolarizing compound selected from the group consistingof mercuric sulfate and lead sulfate thoroughly mixed with non-reactiveconductive material selected from the group consisting of graphite andcarbon black to which organic binder is added, and where the electrodesare separated by a plastic spacer.

References Cited by the Examiner UNlTED STATES PATENTS 2,783,291 2/57Gold 13G-90 2,814,664 11/57 Ruben 136-119 2,863,933 12/58 Minnick et al136-6 2,930,829 3/60 .lacquier 136-143 2,937,219 5/60 Minnick et al136-6 3,083,252 3/63 Meyers 13G-153 X WNSTON A. DGUGLAS, PrimaryExaminer'.

MURRAY TILLMAN, JOHN A. MACK, Examiners.

